1. Field of the Invention
The present invention relates to a motor control apparatus and a motor control method.
2. Description of the Related Art
There are motor control apparatuses known in the related art that normally implement sine wave PWM (pulse width modulation) control so as to achieve higher motor efficiency and implement rectangular wave control in a high-speed, high-torque range over which the sine wave PWM control cannot be implemented with ease. Such motor control apparatuses include one that achieves a continuous switch between the sine wave PWM control and the rectangular wave control by regarding the rectangular wave as a sine wave with an infinite amplitude and by simultaneously changing the phase and the amplitude in order to reduce the extent of the torque fluctuation occurring when switching between the sine wave and the rectangular wave control (see Japanese Laid-Open Patent Publication No. H11-285288).
However, when the operation is switched from the sine wave PWM control to the rectangular wave control or from the rectangular wave control to the sine wave PWM control in the motor control apparatus in the related art described above, the motor current does not change seamlessly, causing fluctuation in the rotation speed and the torque of the motor. If a fluctuation of the motor current, the motor rotation speed or the source voltage occurs at the time of the control switch, a trailing delay occurs as a result of the fluctuation.
It would be desirable to provide a motor control apparatus and a motor control method that achieve a smooth switch between the sine wave control and the rectangular wave control.
A motor control apparatus according to the present invention comprises a sine wave voltage drive device that generates a sine wave AC voltage and applies the sine wave AC voltage to a motor, a rectangular wave voltage drive device that generates a rectangular wave AC voltage and applies the rectangular wave AC voltage to the motor, a speed detection device that detects a rotation speed of the motor, a control switching device that switches to either the sine wave voltage drive device or the rectangular wave voltage drive device based upon the motor rotation speed and a torque command value and an intermediate wave voltage drive device that generates an AC voltage forming an intermediate wave achieved by combining a sine wave and a rectangular wave and applies the intermediate wave AC voltage to the motor when a switch between the sine wave voltage drive device and the rectangular wave voltage drive device is effected by the control switching device.
A motor control apparatus according to the present invention comprises a speed detection device that detects a rotation speed of a motor, an intermediate wave synthesizing device that generates an intermediate wave by combining a sine wave and a rectangular wave so as to set a rectangular wave component contained in the intermediate wave to 0 when the motor rotation speed and a torque command value are within a specific range and to increase the rectangular wave component contained in the intermediate wave as the motor rotation speed increases and also as the motor torque command value becomes higher when the motor rotation speed and the torque command value are outside the specific range and a drive device that controls an inverter by using the intermediate wave synthesized at the intermediate wave synthesizing device and applies and AC voltage achieving a waveform of the intermediate wave to the motor.
A motor control apparatus according to the present invention comprises a sine wave voltage generating device that implements PWM control based upon a modulation triangular-wave voltage and a sine-wave control voltage, controls an inverter by calculating a PWM control duty command value and generates an equivalent sine wave AC voltage to be applied to a motor, a rectangular wave voltage generating device that generates a rectangular wave AC voltage to be applied to the motor by controlling the inverter, a speed detection device that detects a rotation speed of the motor, a threshold value setting device that sets a PWM control duty threshold value in correspondence to the rotation speed and a motor torque command value and a control switching device that implements control so as to apply the equivalent sine wave AC voltage to the motor when the PWM control duty command value does not exceed the threshold value and to apply the rectangular wave AC voltage to the motor when the PWM control duty command value exceeds the threshold value.
A method of motor control achieved by selecting either a sine wave AC voltage or a rectangular wave AC voltage to be applied to a motor comprises generating an AC voltage forming an intermediate wave by combining a sine wave and a rectangular wave and applying the AC voltage forming an intermediate wave to the motor when a switch between the sine wave AC voltage and the rectangular wave AC voltage occurs.